Hi all,

Please consider this example:
Code :
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <std_lib_facilities_4.h>
using namespace std;
 
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow*);
int main() {
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
 
	   // glfw window creation
	GLFWwindow* window = glfwCreateWindow(800, 600, "Hello OpenGL!", nullptr, nullptr);
	if (window == nullptr)
	{
		cout << "Failed to create GLFW window" << endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
 
	   // glad: load all OpenGL function pointers
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		cout << "Failed to initialize GLAD" << endl;
		return -1;
	}
 
	glViewport(0, 0, 800, 600);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
 
	while (!glfwWindowShouldClose(window))
	{
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		processInput(window);
		glfwSwapBuffers(window);
 
		  //check and call events
		glfwPollEvents();
	}
 
	glfwTerminate();
	return 0;
}
 
//*******************************************
 
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	glViewport(0, 0, width, height);
}
 
//******************************************
 
void processInput(GLFWwindow* window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}

1- Why do we need glfwPollEvents(); here? Apparently processInput(window); gets our Esc key when pressed.

2- This function:
Code :
void framebuffer_size_callback(GLFWwindow* window, int width, int height) 
           { ** *
               glViewport(0, 0, width, height); 
          }

is called by this statement: glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); Here the parameters width and height aren't set, so how does the function above set its arguments to be used by glViewport?